Recent progress in large tunnel magnetoresistance junctions T. - - PowerPoint PPT Presentation

Recent progress in large tunnel magnetoresistance junctions

• 1. A little review of MTJs
• 2. Heusler electrode TMR junctions

・ Relationship between degree of order and TMR ratio ・ Temperature and bias dependences of TMR ratio

• 3. Applications of TMR junctions (Gilbert damping

constant α)

• T. Miyazaki1), Y. Sakuraba2), D.Watanabe3) S. Tsunegi3), M. Oogane3) and Y. Ando3)

March 6, 2008 1 WPI Advanced Institute for Materials Research Tohoku University, Sendai Japan. 2 Institute for Materials Research, Tohoku University，Sendai, Japan. 3 Department of Applied Physic, Tohoku University, Sendai, Japan. Aachen, Germany JST-DFG Workshop on Nanoelectronics

• 1. A little review of MTJs

History of TMR research

(Typical reports)

• Julliere (Phys. Lett., 54A,225(1975))

Gd-O

• T.Miyazaki et al. (J.Magn.Magn.Mater.139,L231(1995)) Al-O
• J.S.Moodera et al. (Phys.Rev.Lett., 74, 3273(1995)) Al-O
• S.Yuasa et al. (Jpn.J.Appl.Phys., 43, L588(2004))

MgO

• S.S.P.Parkin et al. (Nature Materials, 3, 863(2004))

MgO

• Y.Sakuraba et al. (Appl.Phys.Lett., 88, 192508(2006)) Heusler
• N.Tezuka et al. (Appl.Phys. Lett.,89, 252508-1(2006)) Heusler
• T.Ishikawa et al. (Appl.Phys.Lett.,89,192505-1(2006)) Heusler

H (Oe) M (arb.units)

• 100
• 50

50 100 (b)

• 100
• 50

50 100 H (Oe) 0.006 0.007 0.008 20 10 RS (a)

R (Ω) ΔR / RS (%)

at R. T.

Magnetoresistance curve (a) and magnetic hysteresis loop (b) for Fe/Al2O3/Fe junction Fe/Al2O3/Fe

T.Miyazaki and N.Tezuka, J.3M, 139,L2341(1995).

• 200
• 100

100 200 100 200 300

MR比 ( % ) H ( Oe ) 293 K 20 K MR = 245 % MR = 180 %

Yuasa et al. Nature Materials 3 (2004).

Fe(001)/MgO(001)/Fe(001)

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

20 40 60 80 100 120 140 160 180 200

Highest TMR ratio (%)（at RT）

Year

MIT Tohoku IBM Fujitsu IBM Tohoku INESC Fujitsu NVE ANELVA Sony CNRS CSIC MPI

AIST AIST

Al-O barrier MgO barrier

100 200 300 400 500 600 1994 1996 1998 2000 2002 2004 2006 2008

Year TMR ratio (%)

, MgO-barrier MTJs AlO-barrier MTJs

CanonANELVA CanonANELVA & AIST & AIST AIST AIST IBM

IT IT-

• program

program

• f RR2002
• f RR2002

AIST AIST

500%@RT (1010%@5K)

AIST AIST Tohoku Univ. Tohoku Univ.

(Ikeda et al. Tohoku Univ.)

• 2. TMR in Heusler alloy

electrode junction

Annalen der Physik Band 19 (1934) 155-201.

Functions of Heusler Compounds

• Magnetic material:

Cu2MnAl

• Halfmetallic ferromagnet: NiMnSb
• Magneto-optical:

PtMnSb

• Magneto-mechanic:

Ni2MnGa

• Superconductor:

Pd2YSn Semiconductor: CoTiSb

• Heavy fermion:

Fe2VAl

• Li-conductor:

LiMnSb

• Magneto-electronic:

Co2FeSi

• Thermo-electric:

TiNiSn

• Magneto-caloric:

CoMnSb:Nb 1905 1983 2001

From

• Prof. Felser

・Spintronics Material : Co2MnSi

Ｘ

7

Tunneling barrier

UHV magnetron sputtering system (P < 1 x 10-7Pa)

Crystallized

We successfully fabricated highly ordered Co2MnSi

Giant TMR ratio over 1000% at LT is possible in CMS/(Mg/Al/Mg)-O/CMS structure

93%@RT

CoFeB/MgO/CoFeB

Ikeda et al. JJAP 44 (2005) L1442

Large temperature dependence of TMR ratio should be solved.

To be published in Phys. Rev. Lett.

LSDA : Local Spin Density Appro. DMFT : Dynamical Mean Field Theory

• 3. Applications of

TMR junction

Application of large TMR junctions

• MRA (Magnetization switching : bit and word lines)
• Spin-RAM (Switching by spin transfer torque)
• Magnetic reading head of HDD
• GPS sensor devices
• High frequency oscillator devices

electron flow

Ferro1 Ferro2 Spacer

Spin-transfer switching (STS)

Slonzcewski, JMMM159 (1996)L1

トルク R Current Parallel Anti-parallel

STS + TMR

Magnetization switching by direct current

G bit + low power MRAM New devices

field current

Target

precession

0.01 0.1 1 10 Writing current (mA) 10 100 1000 Memory cell size (nm) Current

Spin transfer switching

CMOS

Issues for Spin-RAM

Current field switching CMOS maximum IDS 1 mA/1 μm J = 5×106 A/ cm2 1×106 A/ cm2 5×105 A/ cm2 Aspect ratio = 2

Gbit Mbit

Switching current : JC0 ~ 5×105 A/cm2

Issues for device application

) cos 1 ( 2 1 ) , (

2

θ θ P P P gtunnel + =

[ ]

2 / ) 2 ( ) , (

S eff ext B S c

M H H P g d eM J π θ μ αγ + ± =

±

⎭ ⎬ ⎫ ⎩ ⎨ ⎧ − = ln 1 τ τ p

u B c c

V K T k J J

Thermal stability

JC0 ~ 5×105 A/cm2

Requirement for devices

Junction Resis. 20 kΩ Area 80×160 nm2 R・A ~ 200 Ωμm2 Pulse width τ0 ~ 1 ns

• R. H. Koch, PRL92(2004)088302-1
• J. C. Slonzcewski, JMMM159 (1996)L1 , PRB71(2005)024411

α : damping constant, Ms : saturation magnetization d : free layer thickness, P : spin polarization of pinned layer

Switching current density

H

Microwave bridge

h

X-band (9.7 GHz)

TE102 model cavity

Kerr effect P u m p P r

• b

e Hpulse Photo-switch H

s t a t i c

2 4 6 Time (ns) My/Ms Line width : ΔHPP

H

Measurement of damping constant α FMR Pump-probe method

2

; ( 2) ; g-2 L/S

S

G M G g αγ ≡ ∝ − ≈

(g-2)2 G (sec-1)

Fe-Co Fe-Ni Co-Ni

0.01 0.02 0.03 0.04 2 4 6 (ｘ 108)

CoFeB

Co2Mn(Al,Si) YIG Co Ni Fe Co2MnAl (B2) Co2MnSi (B2) Wakitani et al. Oogane

⊗

Co2Fe(Mn)Si (L21) α=0.004

Summary

• TMR ratio more than 100 % (200 %) at room

temperature has been obtained for Heusler electrode and Al-O (MgO) barrier tunnel junctions.

• Damping constant α of Heusler alloys

(Co2MnSi) is 0.004.

• Rapid decrease of TMR ratio with raising

temperature and increasing voltage can be explained by Non-quasiparticle states.

• Heusler alloys are excellent candidate for

spintronics materials.

A part of this work was supported by the IT Program of the Research Revolution 2002 (RR2002) by a Grant-in-Aid for Scientific Research from Ministry of Education, Culture, Sports, Science and Technology of Japan and by Strategic Information and Communications R&D Promotion Programme (SCOPE) by Ministry of Internal Affairs and Communications and NEDO Spintronics nonvolatile devices project. ACKNOWLEDGMENTS